Search

We present herein the preparation of four different hydrogels based on the pseudopeptide gelator Fmoc-l-Phe-d-Oxd-OH (Fmoc=fluorenylmethyloxycarbonyl), either by changing the gelator concentration or adding graphene oxide (GO) to the water solution. The hydrogels have been analysed by rheological studies that demonstrated that pure hydrogels are slightly stronger compared to GO-loaded hydrogels. Then the hydrogels efficiency to trap the cationic methylene blue (MB) and anionic eosin Y (EY) dyes has been analyzed. MB is efficiently trapped by both the pure hydrogel and the GO-loaded hydrogel through π-π interactions and electrostatic interactions. In contrast, the removal of the anionic EY is achieved in less satisfactory yields, due to the unfavourable electrostatic interactions between the dye, the gelator and GO., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Four new low molecular weight hydrogelators (LMWGs) have been prepared in multigram scale and their attitude to form hydrogels has been tested. The gelation trigger is pH variation. The resulting gels have been characterized with several techniques: measurement of the melting points (T(gel)), transparency, gelation time, and viscoelastic properties, together with ECD analysis. Among them, Fmoc-L-Tyr-D-Oxd-OH 1 is an excellent gelator that leads to the preparation of strong, transparent, and viscoelastic gels, by pH variation. UV-visible analyses have demonstrated that the gels obtained with the LMWG 1 possess high transparency, with a transmittance up to 25.6% at a wavelength of 600 nm. Results of the amplitude sweep experiments showed that the elastic response component (G') was approximately an order of magnitude larger than the viscous component, indicating an elastic rather than viscous attitude of the gels, confirmed by the frequency independence of G' and G″ values, in the range from 0.1 to 100 rad·s(-1). The thermal behavior of gel obtained from Fmoc-L-Tyr-D-Oxd-OH 1 was characterized performing an "ad hoc" rheological temperature sweep experiment, that indicated that G' remained almost constant from 23 °C up to about 65 °C while G″ increased in the same temperature range. At higher temperatures, both G' and G″ values started to slightly decrease without displaying a crossover point.